Substrate having a mark formed on a surface thereof by a CO2 laser beam

ABSTRACT

The present invention relates to a CO 2  laser-transparent material having a mark on the surface thereof and the method for making the same. The method includes the following steps: providing a first substrate, which has a top surface and a bottom surface; providing a second substrate which has a top surface; putting the bottom surface of the first substrate on the top surface of the second substrate; irradiating a CO 2  laser beam to the top surface of the second substrate by passing through the top surface and the bottom surface of the first substrate; and forming a mark on the bottom surface of the first substrate. The material of the mark is oxide of the second substrate or the same as the material of the second substrate. Whereby the cheap CO 2  laser is utilized to form the mark on the first substrate, and the mark can be erased easily by a proper chemical for recycling the first substrate.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Divisional of application Ser. No. 12/839,186filed on Jul. 19, 2010, now U.S. Pat. No. 8,557,715, which claimspriority under 35 U.S.C. §119(a) on Patent Application No. 095124898,filed in Taiwan, Republic of China on Jul. 7, 2006. The entire contentsof all of the above applications are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of Invention

The present invention relates to a marking method, and moreparticularly, to a method for forming a mark on the surface of a CO₂laser-transparent material.

2. Description of the Related Art

At present, laser is a marking technique widely used in the industry,and is applied to materials such as plastic, rubber, ceramics, metal,and silicon wafer. Compared with conventional manners, for example,mechanical engraving, chemical etching, screen printing, and inkprinting, laser marking has the advantages of rapid production, highflexibility, and being controllable via a computer system. In addition,a prominent characteristic of laser marking is the permanence of themark generated by a laser on the surface of a workpiece.

There are many kinds of lasers and the femtosecond laser, excimer laser,or Nd:YAG laser are mostly used in silicon wafer marking. However, theselasers are generally very expensive, and the processing mechanismthereof is ablating the surface of the silicon wafer with a laser beamof high energy, which may damage the surface structure of the siliconwafer and result in many flying minute particles, i.e., the so-called“splashing fragments”. The fragments are prone to be attached to thesilicon wafer, thus becoming difficult to erase. When proceeding to thesubsequent device circuit process, a grip head is used to fix the edgeof the silicon wafer. However, the clamping force is easy to make theresidual fragments fall off and cause another splashing, which not onlycontaminates the process, but also severely affects the yield andquality of the product. Moreover, these lasers remove the surface of theproduct to form a mark, so the mark cannot be re-made, and once markedincorrectly, the product will be abandoned for uselessness, and thematerial cannot be recycled.

Moreover, in the conventional fabrication process of semiconductordevices, the marking process is generally performed after the siliconwafer is diced into chips. As the technique is being constantly updatedand the integrated circuits are becoming lighter, thinner, and smaller,the processing technique has also evolved into dicing the wafer aftermarking, so as to improve the efficiency of production and operation.However, as the size of the silicon wafer is getting larger, thethickness thereof stays unchanged or becomes smaller. Therefore, whenthe surface of the silicon wafer is ablated with a laser beam of highenergy, a large amount of stress is easily accumulated on the surface ofthe silicon wafer, resulting in deformation and warping thereof. Thoughthe stress can be eliminated by high temperature annealing, the basicproperty of the silicon wafer is greatly affected, which isdisadvantageous for the subsequent production.

In view of the disadvantages of using the above lasers, ROC (TW) PatentPublication No. 350797 provides a processing method for removingparticles in the semiconductor industry, and particularly for removingsilicon particles generated after making a mark with a laser on thechip. In the method, the wetting and catalytic effects are achieved withthe hydroxyl in the aqueous ammonia, so as to oxidize the particles. ROC(TW) Patent Publication No. 434749 provides a marking method, in whichthe wafer mark can be recovered after a chemical-mechanical polishingprocess is performed on the wafer, and no silicon particles aregenerated during the marking. According to the method, the photoresistis exposed with a fiber optic cable, so as to form a mark on thephotoresist, and a wafer mark is formed subsequently by etching with thephotoresist having a mark formed thereon as a mask. ROC (TW) PatentPublication No. 359885 provides a method, in which a mark pattern on atape is defined with a laser beam, then the tape is adhered onto asilicon wafer, then the pattern is transferred to the wafer by a wet ordry process, and the tape is finally stripped to finish making a mark onthe silicon wafer. The above method can avoid causing splashingfragments.

In Japanese Patent Publication No. 11-260675, a spot-shaped mark isfabricated on a silicon wafer with a laser, and a layer of transparentthin film is formed thereon. When a laser beam passes through thetransparent thin film to make the spot-shaped mark regionally melt anddeformed, a plurality of spot-shaped marks can be formed. This methodcan prevent the splashing fragments generated during the laserprocessing from being attached to the silicon wafer, and the definitionand visibility are ensured by the shape of these spot-shaped marks.

ROC (TW) Patent Publication No. 1233197 provides a chip scale mark and amarking method of the same. According to the method, when a laser beamablates the surface of a silicon wafer, the chip size mark is used tostably keep the laser system and the marking distance between the wafersby removing the wafer warp on the wafer support. ROC (TW) PatentPublication No. 200538304 provides a method for making a mark by formingan interference fringe on a body to be marked with a laser beam.

Therefore, it is necessary to provide a method for forming a mark on thesurface of a CO₂ laser-transparent material e.g. silicon to solve theabove problems.

SUMMARY OF THE INVENTION

The present invention provides a method for forming a mark. The methodincludes the following steps: providing a first substrate, which has atop surface and a bottom surface; providing a second substrate, whichhas a top surface; disposing the bottom surface of the first substrateon the top surface of the second substrate; irradiating a CO₂ laser tothe top surface of the second substrate by passing through the topsurface and the bottom surface of the first substrate; and forming amark on the bottom surface of the first substrate. The material of themark is oxide of the second substrate or the same as the material of thesecond substrate.

The present invention also provides a method for forming a mark. Themethod includes the following steps: providing a first substrate, whichhas a top surface and a bottom surface; providing a second substrate,which has a top surface; forming a metal film on the top surface of thesecond substrate; disposing the bottom surface of the first substrate onthe metal film; irradiating a CO₂ laser to the metal film by passingthrough the top surface and the bottom surface of the first substrate;and forming a mark on the bottom surface of the first substrate. Thematerial of the mark is a mixture. The mixture includes metal and thesecond substrate.

The present invention further provides a substrate having a mark on thesurface thereof. A substrate has a surface, wherein the material of thesubstrate is a CO₂ laser-transparent material; and a mark located on thesurface of the substrate, wherein the mark is formed by a CO₂ laser, andthe material of the mark is a CO₂ laser-absorption material.

In the present invention, the CO₂ laser with a light wavelength of 10.6μm is not absorbed by the first substrate, e.g. silicon material, solarenergy wafer or solar energy chip, but can pass through the firstsubstrate and absorbed by the metal film and the second substrate, e.g.glass, silica, metal oxide, ceramics, nitride, carbide or polymethylmethacrylate (PMMA). Thus, the mark is formed by the re-solidificationof the melted and/or vaporized material of the second substrategenerated by the second substrate under the input irradiation energy ofthe CO₂ laser. Alternatively, the mark is formed by there-solidification of the melted and/or vaporized mixture generated bythe metal film and the second substrate under the input irradiationenergy of the CO₂ laser. The CO₂ laser is the cheapest laser amongvarious lasers, so the present invention provides a method for markingthe CO₂ laser-transparent material, such as the wafer, in a rapid andsimple way, which costs less, consumes less energy, and has highreliability and quality. Moreover, stress can be avoided by utilizinglow energy means of marking, such that the first substrate, e.g. siliconmaterial, solar energy wafer or solar energy chip, will not be deformedor warped. Further, the present invention does not utilize the laserbeam in such a way of ablation, therefore the first substrate will notbe damaged after the processing, and no splashing fragments and dustswill be generated, thereby abating pollution and improving yield.Besides, it is not necessary to use a mask, and the photolithographyprocess may not be affected, such that the capacity is improved.Additionally, when marked incorrectly with other lasers, the surface ofthe wafer product is usually damaged. However, in the present invention,the CO₂ laser is employed, and a common chemical can be used to erasethe incorrect mark so that the first substrate, e.g. silicon material,solar energy wafer or solar energy chip, may be recycled.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a method for forming a mark accordingto a first embodiment of the present invention;

FIG. 2 is a photograph of the silicon wafer having a mark on the surfacethereof formed according to an example of the experiment in the firstembodiment of the present invention, in which the mark is constituted byletters;

FIG. 3 is a photograph of the silicon wafer having a mark on the surfacethereof formed according to the example of the experiment in the firstembodiment of the present invention, in which the mark is constituted bytotems and random codes;

FIG. 4 is a photograph of the first substrate having a mark on thesurface thereof formed according to another example of the experiment inthe first embodiment of the present invention, in which the mark isconstituted by four Chinese character;

FIG. 5 is a photograph showing the material composition of the markanalyzed according to the EDX analysis;

FIG. 6 is a photograph showing the material of the portion without themark analyzed according to the EDX analysis;

FIG. 7 is a photograph showing the mark measured by an alpha-stepprofilometer;

FIG. 8 is a schematic diagram of a method for forming a mark accordingto a second embodiment of the present invention; and

FIG. 9 is a schematic diagram of a substrate having a mark on thesurface thereof according to a third embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a schematic diagram of a method for forming a mark accordingto a first embodiment of the present invention. In this embodiment,firstly, a first substrate 11 is provided, which has a top surface 111and a bottom surface 112. In this embodiment, the material of the firstsubstrate 11 is a CO₂ laser-transparent material. That is, the CO₂ lasertransmittance of the first substrate 11 is higher than the CO₂ laserabsorptance of the first substrate 11. The CO₂ laser transmittance ofthe first substrate 11 can be over 50 percent. Preferably, the CO₂ lasertransmittance of the first substrate 11 is over 80 percent. In otherwords, the absorption band at 10.6 μm of the first substrate 11 is weakin the IR spectrum due to low absorption coefficient. Herein, the firstsubstrate 11 can be a silicon wafer, which can be pure silicon or have amulti-layered thin film. Additionally, the first substrate 11 can alsobe a silicon chip, a solar energy wafer or a solar energy chip. In thisembodiment, the first substrate 11 is disposed with a polished surfacefacing upward (i.e., the top surface 111 of the first substrate 11 is apolished surface) or with a rough surface facing upward (i.e., thebottom surface 112 of the first substrate 11 is a polished surface).Alternatively, the first substrate 11 can be a double-side polishedsubstrate (i.e., the top surface 111 and the bottom surface 112 of thefirst substrate 11 both are polished surfaces). Preferably, the bottomsurface 112 of the first substrate 11 is a polished surface.

Next, a second substrate 12 is provided, which has a top surface 121. Inthis embodiment, the material of the second substrate 12 is a CO₂laser-absorption material. That is, the CO₂ laser absorptance of thesecond substrate 12 is higher than the CO₂ laser transmittance of thesecond substrate 12. The CO₂ laser absorptance of the second substrate12 can be over 50 percent. Preferably, the CO₂ laser absorptance of thesecond substrate 12 is over 80 percent. In other words, the absorptionband at 10.6 μm of the second substrate 12 is intense in the IR spectrumdue to high absorption coefficient. Herein, the material of the secondsubstrate 12 can be glass, silica, metal oxide, ceramics, nitride,carbide or polymethyl methacrylate (PMMA). Afterward, the bottom surface112 of the first substrate 11 is disposed on the top surface 121 of thesecond substrate 12, and the top surface 121 of the second substrate 12is closely attached to the bottom surface 112 of the first substrate 11.In this embodiment, a clamp (not shown) is used to clamp the secondsubstrate 12 and the first substrate 11, such that the top surface 121of the second substrate 12 is closely attached to the bottom surface 112of the first substrate 11. Next, the second substrate 12 and the firstsubstrate 11 are disposed on a support platform 18.

After that, a CO₂ laser 14 is provided by a CO₂ laser generator 13. TheCO₂ laser 14 is focused on the first substrate 11 through a focusingmechanism having a reflecting mirror 15 and a focusing lens 16. Then,the CO₂ laser 14 is irradiated to the top surface 121 of the secondsubstrate 12 by passing through the top surface 111 and bottom surface112 of the first substrate 11 since the CO₂ laser 14 is not absorbed bythe first substrate 11, but the CO₂ laser 14 is absorbed by the secondsubstrate 12. The irradiated portion of the second substrate 12 ismelted and/or vaporized, and then re-solidified on the bottom surface112 of the first substrate 11. Therefore, the part of the secondsubstrate 12 is disposed on the bottom surface 112 of the firstsubstrate 11 to form the mark. Accordingly, in this embodiment, the markis not an-etched groove, but a protrusion. The material of the mark isan oxide of the second substrate 12 or same as the material of thesecond substrate 12. The mark is formed by the re-solidification of themelted and/or vaporized material of the second substrate 12 generated bythe second substrate 12 under the input irradiation energy of the CO₂laser 14 or formed by the oxide of the second substrate 12.

In addition, the mark is formed by irradiating the CO₂ laser 14 lessthan five passes to prevent the CO₂ laser 14 from damaging the firstsubstrate 11, especially the top surface 111. Moreover, the mark can beof any shape, such as a numeral, a letter or a totem.

Further, in this embodiment, the CO₂ laser 14 can be focused on theinterior, the top surface 111 or the bottom surface 112 of the firstsubstrate 11. The focusing position of the CO₂ laser 14 can be adjustedwith the reflecting mirror 15 and the focusing lens 16, or controlled byadjusting the direction of Z-axis of the support platform 18, and thetwo methods for adjusting focusing position can be integrated. Inaddition, the focusing position of the CO₂ laser 14 would affect theeffective energy density for melting/evaporating the second substrate12. Herein, the effective energy density of focusing position is higherthan other divergent defocus position. In FIG. 1, the focusing positionis on the top surface 111 of the first substrate 11 which will hashigher effective energy density than the interior or the bottom surface112 of the first substrate 11. We can also adjust the focusing positionat the bottom surface 112 of the first substrate 11 for more effectiveenergy density for marking. In this embodiment, the CO₂ laser 14 isfocused on the top surface 111 of the first substrate 11. By adjustingappropriate laser processing parameters, such as, the power of the CO₂laser source, scanning speed, pass number (about less than five passes),and together by scanning the laser spot or moving the support platform18, a desired mark shape can be achieved.

Additionally, if a part or the whole of the mark is undesired orincorrect, a cleaning chemical can be used to directly erase the mark.The chemical cleaning agent can be hydrofluoric acid (HF), bufferedoxide etching (BOE), or a general chemical capable of erasing oxide.

Hereinafter is an example of the experiment according to thisembodiment. The first substrate 11 is a silicon wafer and the secondsubstrate 12 is a glass substrate. The processing condition of thisexample is: the thicknesses of the first substrate 11 and the secondsubstrate 12 are both 500 μm; the power of the CO₂ laser 14 is 21 W andthe focus point thereof is set on the top surface 111 of the firstsubstrate 11; the mark is directly formed by irradiating the CO₂ laser14 once at a scanning speed of 5 mm/sec, and the processing result isshown in FIG. 2.

As shown in FIG. 2, the silicon wafer includes a silicon material 11 anda mark 17. The silicon material 11 has a surface 112 (i.e., the bottomsurface 112 in FIG. 1). In this example, the surface 112 is a polishedsurface, and it is to be understood that the surface 112 can also be arough surface. The mark 17 is located on the surface 112 of the siliconmaterial 11, and the mark 17 is silicon oxide, which can be constitutedby numerals, letters, or totems. In this example, the mark 17 isconstituted by letters of “NCKU.” Also, the mark is other totems orrandom codes, as shown in FIG. 3.

Further, hereinafter is another example of the experiment according tothis embodiment. In this example, the first substrate 11 is a siliconwafer and the second substrate 12 is a pyrex glass substrate. Then, thefirst substrate 11 and the second substrate 12 are irradiated andscanned by the CO₂ laser one time. As a result, a four Chinese charactermark is formed on the surface of the first substrate 11, as shown inFIG. 4. And, the material of the mark comprises Si, O and Na, as shownin the EDX analysis in FIG. 5, which consists of the primary materialcomposition of the Pyrex glass. The material of the portion without themark is only silicon (Si), as shown in the EDX analysis in FIG. 6. Theprofile of the mark measured by an alpha-step profilometer is shown inFIG. 7, which confirms that the mark protrudes from the surface of thesilicon wafer.

FIG. 8 is a schematic diagram of a method for forming a mark accordingto a second embodiment of the present invention. In this embodiment,firstly, a first substrate 21 is provided, which has a top surface 211and a bottom surface 212. In this embodiment, the material of the firstsubstrate 21 is a CO₂ laser-transparent material. That is, the CO₂ lasertransmittance of the first substrate 21 is higher than the CO₂ laserabsorptance of the first substrate 21. The CO₂ laser transmittance ofthe first substrate 21 can be over 50 percent. Preferably, the CO₂ lasertransmittance of the first substrate 21 is over 80 percent. In otherwords, the absorption band at 10.6 μm of the first substrate 21 is weakin the IR spectrum due to low absorption coefficient. Herein, the firstsubstrate 21 is a silicon wafer, which can be pure silicon or have amulti-layered thin film. Additionally, the first substrate 21 can alsobe a silicon chip, a solar energy wafer or a solar energy chip. In thisembodiment, the first substrate 21 is disposed with a polished surfacefacing upward (i.e., the top surface 211 of the first substrate 21 is apolished surface) or a rough surface facing upward (i.e., the bottomsurface 212 of the first substrate 21 is a polished surface).Alternatively, the first substrate 21 can be a double-side polishedsubstrate (i.e., the top surface 211 and the bottom surface 212 of thefirst substrate 21 both are polished surfaces). Preferably, the bottomsurface 212 of the first substrate 21 is a polished surface.

Next, a second substrate 22 is provided, which has a top surface 221. Inthis embodiment, the material of the second substrate 22 is a CO₂laser-absorption material. Herein, the material of the second substrate12 can be glass, silica, metal oxide, ceramics, nitride, carbide orpolymethyl methacrylate (PMMA). That is, the CO₂ laser absorptance ofthe second substrate 22 is higher than the CO₂ laser transmittance ofthe second substrate 22. The CO₂ laser absorptance of the secondsubstrate 22 can be over 50 percent. Preferably, the CO₂ laserabsorptance of the second substrate 22 is over 80 percent. In otherwords, the absorption band at 10.6 μm of the second substrate 22 isintense in the IR spectrum due to high absorption coefficient.Afterward, a metal film 27 is formed on the top surface 221 of thesecond substrate 22. Preferably, the metal film 27 is formed on the topsurface 221 of the second substrate 22 by coating, and the material ofthe metal film 27 can be selected from a group consisting of aluminum,titanium, chromium, tantalum, nickel, iron, cobalt, vanadium, tungsten,zirconium, zinc, copper, silver, and gold. The thickness of the metalfilm 27 can be between 10-1000 nm. Preferably, the material of the metalfilm 27 is aluminum, titanium, chromium, tantalum, nickel, iron, cobalt,vanadium, tungsten, zirconium or zinc, and the thickness thereof isbetween 30-80 nm.

Afterward, the bottom surface 212 of the first substrate 21 is disposedon the metal film 27 coated on the second substrate 22. And the topsurface 221 of the second substrate 22, the metal film 27, and thebottom surface 212 of the first substrate 21 are closely attached. Inthis embodiment, a clamp (not shown) is used to clamp the secondsubstrate 22 and the first substrate 21. Next, the second substrate 22and the first substrate 21 are disposed on a support platform 28.

Afterward, a CO₂ laser 24 is provided by a CO₂ laser generator 23.Finally, the CO₂ laser 24 is focused on the first substrate 21 through afocusing mechanism having a reflecting mirror 25 and a focusing lens 26.Then, the CO₂ laser 24 is irradiated to the metal film 27 by passingthrough the top surface 211 and bottom surface 212 of the firstsubstrate 21 since the CO₂ laser 24 is not absorbed by the firstsubstrate 21, but the CO₂ laser 24 is absorbed by the metal film 27 andthe second substrate 22. When the CO₂ laser 24 irradiates to the metalfilm 27, the heat caused by the CO₂ laser can be conducted to the topsurface 221 of the second substrate 22 to cause the correspondingportion of the second substrate 22 melt and/or vaporize. Of course, whenthe metal film 27 is thin enough, the CO₂ laser 24 may pass through themetal film 27 and irradiate to the top surface 221 of the secondsubstrate 22. Accordingly, the irradiated portion of the metal film 27and the corresponding portion of the second substrate 22 are meltedand/or vaporized, and then re-solidified on the bottom surface 212 ofthe first substrate 21. Therefore, the part of the metal film 27 and thesecond substrate 12 are disposed on the bottom surface 212 of the firstsubstrate 21 to form the mark. The mark formed by growing or depositing,which is formed by utilizing the input irradiation energy of the CO₂laser to melt and/or vaporize the metal film 27 and the top surface 221of the second substrate 22, and then re-solidifying the both. Thus, themark is not an etched groove, but a protrusion. The material of the markis a mixture, and the mixture includes metal and the second substrate.Of course, the mixture may also include metal oxide or the oxide of thesecond substrate 22.

Moreover, the mark can be of any shape, such as a numeral, a letter, ora totem. In addition, the mark is formed by irradiating the CO₂ laser 24less than five passes to prevent the CO₂ laser 24 from damaging the topsurface 211 of the first substrate 21.

Further, in this embodiment, the CO₂ laser 24 can be focused on theinterior, the top surface 211 or the bottom surface 212 of the firstsubstrate 21. The focusing position of the CO₂ laser 24 can be adjustedwith the reflecting mirror 25 and the focusing lens 26, or controlled byadjusting the direction of Z-axis of the support platform 28, and thetwo methods for adjusting focusing position can be integrated. Inaddition, the focusing position of the CO₂ laser 24 would affect theeffective energy density for melting/evaporating the second substrate22. Herein, the effective energy density of focusing position is higherthan other divergent defocus position. In FIG. 8, the focusing positionis on the top surface 211 of the first substrate 21 which will hashigher effective energy density than the interior or the bottom surface212 of the first substrate 21. We can also adjust the focusing positionat the bottom surface 212 of the first substrate 21 for more effectiveenergy density for marking. In this embodiment, the CO₂ laser 24 isfocused on the top surface 211 of the first substrate 21. By adjustingappropriate laser processing parameters, such as, the power of the CO₂laser source, scanning speed pass number (about less than five passes),and together by scanning the laser spot or moving the support platform28, a desired mark shape can be achieved.

Additionally, if a part or the whole of the mark is undesired orincorrect, a cleaning chemical can be used to directly erase the mark.The chemical cleaning agent can be hydrofluoric acid (HF), bufferedoxide etching (BOE), or a general chemical capable of erasing oxide.

FIG. 9 is a schematic diagram of a substrate having a mark on thesurface thereof according to a third embodiment of the presentinvention. In this embodiment, a substrate 31 has a surface 311, and thematerial of the substrate 31 is a CO₂ laser-transparent material. Thatis, the CO₂ laser transmittance of the substrate 31 is higher than theCO₂ laser absorptance of the substrate 31. The CO₂ laser transmittanceof the substrate 31 can be over 50 percent. Preferably, the CO₂ lasertransmittance of the substrate 31 is over 80 percent. In other words,the absorption band at 10.6 μm of the substrate 31 is weak in the IRspectrum due to low absorption coefficient. A mark 32 is located on thesurface 311 of the substrate 31. Herein, the mark 32 is formed by a CO₂laser, and the material of the mark 32 is a CO₂ laser-absorptionmaterial. That is, the CO₂ laser absorptance of the mark 32 is higherthan the CO₂ laser transmittance of the mark 32. The CO₂ laserabsorptance of the mark 32 can be over 50 percent. Preferably, the CO₂laser absorptance of the mark 32 is over 80 percent. In other words, theabsorption band at 10.6 μm of the mark 32 is intense in the IR spectrumdue to high absorption coefficient.

In this embodiment, the material of the mark 32 can be metal, metaloxide, nitride, carbide or silicon oxide or the mixture at leastselected from two of the above material, and the substrate 31 is asilicon wafer or a silicon chip. Herein, the silicon wafer can be puresilicon or has a multi-layered thin film. And, the surface 311 of thesubstrate 31 can be a polished surface. In the embodiment, the featuresand the functions of the substrate 31 and the mark 32 are same as thoseof the first substrate 11 and the mark in the first embodiment, and arealso same as those of the first substrate 21 and the mark in the secondembodiment. Those features and functions are described above. Therefore,unnecessary details are not going to be mentioned here.

In the present invention, the CO₂ laser with a light wavelength of 10.6μm is not absorbed by the first substrate, e.g. silicon material, solarenergy wafer or solar energy chip, but can pass through the firstsubstrate and absorbed by the metal film and the second substrate, e.g.glass, silica, metal oxide, ceramics, nitride, carbide or polymethylmethacrylate (PMMA). Thus, the mark is formed by the re-solidificationof the melted and/or vaporized material of the second substrategenerated by the second substrate under the input irradiation energy ofthe CO₂ laser or the mark is the oxide of the second substrate.Alternatively, the mark is formed by the re-solidification of the meltedand/or vaporized mixture generated by the metal film and the secondsubstrate under the input irradiation energy of the CO₂ laser. Thepresent invention has the following advantages: 1. the CO₂ laser is thecheapest laser among various lasers; 2. the present invention provides amethod for marking the wafer in a rapid and simple way, which costsless, consumes less energy, and has high reliability and quality; 3.stress can be avoided by utilizing low energy, such that the firstsubstrate 11, e.g. silicon material, a solar energy wafer and a solarenergy chip, will not be deformed or warped; 4. the present inventiondoes not adopt the laser beam in the manner of ablation, such that thewafer will not be damaged after the processing, and no splashingfragments and dusts will be generated, thereby abating pollution andimproving the yield; 5. it is not necessary to use a mask, and thephotolithography process may not be affected, such that the capacity isimproved; 6. the first substrate 11 can be a silicon wafer of puresilicon, and can also be a silicon wafer with a multi-layered thin film;7. when marked incorrectly, as other lasers are used in the conventionalart, the incorrect mark cannot be erased from the surface of the damagedproduct (for example, an etched groove is resulted). However, in thepresent invention, a CO₂ laser is used to generate a mark of siliconoxide, and a common chemical can be used to erase the incorrect mark forrecycling the first substrate 11.

While several embodiments of the present invention have been illustratedand described, various modifications and improvements can be made bythose skilled in the art. The embodiments of the present invention aretherefore described in an illustrative but not restrictive sense. It isintended that the present invention should not be limited to theparticular forms as illustrated, and that all modifications whichmaintain the spirit and scope of the present invention are within thescope as defined in the appended claims.

What is claimed is:
 1. A substrate having a mark on the surface thereof,comprising: a substrate having a surface, wherein the material of thesubstrate is a CO₂ laser-transparent material; and a mark located on thesurface of the substrate, wherein the mark is formed by a CO₂ laser, thematerial of the mark is a CO₂ laser-absorption material.
 2. Thesubstrate as claimed in claim 1, wherein the CO₂ laser transmittance ofthe substrate is higher than the CO₂ laser absorptance of the substrate,the CO₂ laser absorptance of the mark is higher than the CO₂ lasertransmittance of the mark.
 3. The substrate as claimed in claim 1,wherein the material of the mark is metal, metal oxide or silicon oxide.4. The substrate as claimed in claim 1, wherein the substrate is asilicon wafer or a silicon chip.
 5. The substrate as claimed in claim 4,wherein the silicon wafer is pure silicon.
 6. The substrate as claimedin claim 4, wherein the silicon wafer has a multi-layered thin film. 7.The silicon material as claimed in claim 1, wherein the surface of thesubstrate is a polished surface.